The present invention relates to an abnormality diagnosis method and apparatus for a gas concentration measuring device for use with an internal combustion engine for combustion control thereof.
Heretofore, in combustion control of an internal combustion engine such as a gasoline engine for reducing CO, NOx and HC contained in the exhaust gas through control of an air-fuel ratio of a mixture of air and fuel to be supplied to the internal combustion engine, there is known such a method of feedback controlling a fuel supply amount in accordance with a concentration of a predetermined gas component contained in an exhaust gas.
As a sensor used for such an air-fuel ratio control, there is known a wide-range air-fuel ratio sensor (also referred to as a UEGO sensor) in which two cells with electrodes are disposed on the opposite sides of a solid electrolytic body made of a material containing zirconia or the like as a major component in a way as to place therebetween a measurement chamber and a measured gas is introduced into the measurement chamber by way of a diffusion resistor for measuring an oxygen concentration in the measured gas, a NOx sensor which is provided with another cell in addition to the above-described two cells so as to be capable of detecting a NOx concentration.
The sensors such as a UEGO sensor can detect a concentration of a predetermined gas component in an exhaust gas over a wide range continuously and thereby improve the accuracy in the combustion control, thus being used widely in these years.
Further, in recent vehicles is used a gas concentration measuring device that performs, during combustion control of an engine using such a gas sensor, an abnormality diagnosis of the gas sensor or a gas sensor controller automatically (a so-called onboard self-diagnosis) and informing a driver of the result of diagnosis.
As such an abnormality diagnosis method of a gas concentration measuring device, there is heretofore known, as disclosed in Japanese Patent Provisional Publication (unexamined) No. 2003-90821, a method of detecting input and output voltages at each electrode of a plurality of cells constituting a gas sensor, and determining whether or not the respective electrode voltages are abnormal for thereby performing an abnormality diagnosis of a short-circuit between a wiring electrically connected to a sensor element and a battery (power source potential), a short-circuit between the wiring and the ground (earth potential) or breakage of the wiring.